I can has cheezburger? Protein cancer risk overblown

Are you middle-aged and partial to cheeseburgers? If so, you may be concerned by a study suggesting you have a much greater risk of dying from cancer than your peers who favour a less protein-rich diet. But not all researchers agree with the study's findings.

Morgan Levine at the University of Southern California in Los Angeles and her colleagues analysed a dietary survey of more than 6300 people in the US aged over 50. Those aged 50-65 at the time of the survey and who had a high-protein diet – one where protein supplied a fifth of calories – were 75 per cent more likely to have died over the next 18 years than peers who only got 10 per cent of their calories from protein.

The high-protein eaters had a cancer death rate four times that of their low-protein peers. Statistical analyses showed that the findings only held for animal protein diets – in other words, protein from meat and dairy rather than beans and pulses.

In a follow-up study in mice, the team also found that animals fed a low-protein diet had a lower incidence of cancer than those on a high-protein diet. The low-protein mice that did develop the disease had slower-growing tumours.

Lots of leaps

But Tim Key, a Cancer Research UK epidemiologist based at the University of Oxford, says the dietary survey is too small to provide any robust conclusions.

Catherine Collins, chief dietician at St George's Hospital, London, doesn't dispute the results in mice, but says the authors make a lot of leaps when trying to apply the findings to humans. What's more, the conclusions are based on a single survey of what people reported eating in the preceding 24 hours. "As a dietician that's worrying," she says. "There are so many errors with the data collection. It implies people's diet doesn't change over 18 years."

Study co-author Valter Longo, also at the University of Southern California, counters that the participants said that the 24 hour period was representative of their diet. "Most people don't change their diet very often," he says.

Different health organisations recommend consuming different amounts of protein. Longo says that people in middle age should try to eat at the lower end of these recommendations.

Collins isn't convinced. "We don't need to do anything different, and nor should we be worried [on the strength of this study]," she says.

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